Semiconductor wafer (“wafer”) fabrication often includes exposing a wafer to a plasma to allow the reactive constituents of the plasma to modify the surface of the wafer, e.g., remove material from unprotected areas of the wafer surface. The wafer characteristics resulting from the plasma fabrication process are dependent on the process conditions, including the plasma characteristics and wafer temperature. For example, in some plasma processes a critical dimension, i.e., feature width, on the wafer surface can vary by about one nanometer per degree Celsius of wafer temperature. It should be appreciated that differences in wafer temperature between otherwise identical wafer fabrication processes will result in different wafer surface characteristics. Thus, a drift in process results between different wafers can be caused by variations in wafer temperature during plasma processing. Additionally, center-to-edge wafer temperature variations can adversely effect a die yield per wafer.
A general objective in wafer fabrication is to optimize a die yield per wafer and fabricate each wafer of a common type in as identical a manner as possible. To meet these objectives, it is necessary to control fabrication parameters that influence the plasma processing characteristics across an individual wafer and among various wafers of a common type. Because plasma constituent reactivity is proportional to temperature, wafer temperature can have an strong influence on plasma processing results across the wafer and among various wafers. Therefore, a continuing need exists for improvements in wafer temperature control during plasma fabrication processes.